The present invention relates to a method of increasing the load supporting capacity of an ice sheet.
Conventionally an ice sheet must attain a specific thickness before it can support a load or loads of given weight and weight distribution. The growth rate and maximum thickness of naturally occurring ice sheets vary from year to year. This variance is influenced by several factors, among which are the ambient air temperature, water temperature, water salinity and local snow fall. People planning on an ice operation such as an ice road, air stop, or a site for an ice-supported drilling rig normally are dependent on the historical average ice thickness to base a decision on whether the ice will be thick enough to support their operation. In some ice covered areas the ice is historically too thin to allow certain types of ice-supported operations. In other areas the ice growth season is such that the ice-supported operation cannot be conducted in the short time span when the ice is at a suitable thickness. Under these conditions various means have been used to increase the ice thickness.
A common approach has been to keep the ice surface free of snow in areas where thick ice is desired. Snow normally acts as a thermal insulator and slows down the ice growth rate. Ice in snow free areas will grow faster and thicker than ice under snow.
Another approach to increasing ice thickness is to flood water on top of the ice and allow it to freeze. This operation is then repeated until the ice has reached a desired thickness. An alternate approach to flooding is to use a spray or sprinkler system to place water on the ice, which results in the ice freezing in thinner layers. The disadvantages to freezing water layers are (1) in using sea water, the brine content of the new ice is high, and thus the new ice is weaker than the orginal ice; and (2) in using sea or fresh water, air bubbles trapped in the ice weakens it. For large loads the required ice thickness is such that spraying and/or flooding methods become impractical because of the time involved in creating the desired ice thickness which in turn reduces the time available for conducting the primary operation.
Another approach has been to place fiberglas matting on top of the ice surface. The surface is then flooded or sprayed with water and allowed to freeze over the matting. This approach misses completely the correct technique to increase the load supporting capacity of the ice matrix because it ignores a very fundamental mechanism of ice failure.